In the past, solar energy collectors, such as the one shown in the U.S. Pat. No. 4,069,812, which is included herein by reference, have provided a very effective and efficient means of converting solar energy into both useful thermal energy by transferring heat to a working fluid and/or useful electrical energy by means of solar cells. As the state of the art advances in solar energy collection, new and more efficient methods of heat collection and solar conversion are constantly being sought. Generally, improved collection systems have either increased the efficiency of the optical system for transforming light rays into usable energy, or improved tracking systems for tracking the sun, or improved thermal systems for collecting and retaining as much heat by a solar receiver as possible. The present invention is primarily concerned with the more efficient collection and the retention of thermal solar energy by providing an improved thermal energy receiver for use within a solar collector device.
Thermal inefficiencies in solar collectors can result from many causes. For example, while solar energy may be efficiently collected and focused upon a thermal receiver, much of that energy may subsequently be lost to the environment surrounding the receiver by radiative, convective and conductive heat transfer, since the receiver will normally operate at a much higher temperature than the environment. Additionally, reflection losses are normally experienced at the black-coated receiver and at the surfaces of transparent covers over the receiver. Even when the solar receiver or absorber is black-coated, reflection losses still occur, albeit to a lesser extent. Moreover, prior attempts to alleviate heat losses in solar thermal receivers have more often than not resulted in a more expensive product which is sometimes deficient in other respects. For example, in order to reduce radiative heat losses, some receivers have utilized black chrome selective coatings which are less durable and more expensive than low-cost black paint.